Historically, garlic (Allium sativum) has been revered as part of a healthful diet. Ancient medical texts from Egypt, Greece, Rome, China, and India prescribed garlic for a number of applications including improving performance, reducing infections, and protection against toxins. These medicinal properties, coupled with its savory characteristics, have made garlic a true cultural icon in many parts of the world.
Garlic, a member of the Alliaceae family of plants, has characteristics similar to onions, leeks, and chives. Its intake is not known with any degree of certainty, since it is not traditionally considered in dietary assessment surveys, and as personal preferences vary considerably. Regardless, consumption varies from region to region, and from individual to individual within a region.[2,3] According to recent United States Deparment of Agriculture (USDA) reports, during any typical day, about 18% of Americans consume at least one food containing garlic. Average intake in the United States has been estimated to be about 0.6 g=week or less, while in some parts of China, it may be as great as 20 g=day.[4,5] Garlic also continues to be one of the top selling dietary supplements in the United States and in several other parts of the world. A recent study in China provided evidence that a reduction in prostate cancer risk occurred when subjects consumed more than 10 g=day compared to those consuming 2.2 g=day or less. While several cellular processes can be modified by garlic or its constituents, it remains unclear who will benefit most from intervention strategies, what factors determine the response, and the minimum quantity and duration needed to bring about a response.
While some appear to be able to tolerate rather large quantities of garlic, e.g., 20 g=day, some may not be as resistant. While a spectrum of adverse reactions has been observed, including contact dermatitis, respiratory distress, gastrointestinal disturbances, bleeding abnormalities, and anaphylactic shock; the overall incidence is quite low. Claims about the health benefits of garlic likely contributed to its clinical usage, especially by individuals flirting with alternative health care strategies. Peng et al. found in their study that about 43% of veteran outpatients were taking at least one dietary supplement along with their prescription medication(s). The most common products included vitamins and minerals, garlic, Ginkgo biloba, saw palmetto, and ginseng. In a comparable study, Adusumilli found that about 57% of patients undergoing elective surgery had used herbal medicine at some point in their life. Echinacea, aloe vera, ginseng, garlic, and Ginkgo biloba were among the most common. Interestingly, one in six in this study used herbal supplements during the month of surgery. Stys et al. reported that patients with a history of myocardial infarction, coronary revascularization, hyperlipidemia, and a family history of coronary artery disease were more likely to use supplements including multivitamins, vitamin E, vitamin C, vitamin B, folate, garlic, calcium, coenzyme Q10, and ginkgo than those without comparable health concerns. Average low-density lipoprotein (LDL), blood pressure, and glycosylated hemoglobin did not differ significantly between users and nonusers.
Garlic is increasingly being recognized to alter several physiological processes that may influence health, including those associated with heart disease and cancer. Preclinical studies provide some of the most convincing evidence that garlic and its related sulfur components can alter a host of biological processes associated with health. Some of the health benefits attributed to the consumption of garlic and associated allyl sulfur components are:
While these results generally support earlier views about garlic’s medicinal properties, there is admittedly considerable variability in response. Unfortunately, a dearth of clinical studies exists for establishing firm conclusions about who might gain most from enhanced consumption.